I. Field
The present invention relates generally to heterogeneous catalysts comprised of platinum and rhodium on a support at least the outer surfaces of which are selected from the group consisting of zirconia, stabilized (doped) zirconia, zirconia-metal oxide composites and mixtures thereof. The catalysts of the present invention are particularly useful for the selective reduction of compositions of the general formula ROOC(CX)yCOOR, where “y” is at least 2, “X” is, independently, selected from the group of hydroxyl, oxo, halo, acyloxy and hydrogen provided that at least one X is not hydrogen, and each “R” is, independently, selected from the group of salt-forming ions, hydrogen and hydrocarbyl or substituted hydrocarbyl or a mono- or di-lactone thereof, to dicarboxylic acids and derivatives thereof. More particularly, the present invention is directed to catalysts for the selective hydrodeoxygenation of such compositions to dicarboxylic acids and/or derivatives thereof, especially adipic acid and/or derivatives thereof.
II. Related Art
Crude oil is currently the source of most commodity and specialty organic chemicals. Many of these chemicals are employed in the manufacture of polymers and other materials. Examples include ethylene, propylene, styrene, bisphenol A, terephthalic acid, adipic acid, caprolactam, hexamethylene diamine, adiponitrile, caprolactone, acrylic acid, acrylonitrile, 1,6-hexanediol, 1,3-propanediol, and others. Crude oil is first refined into hydrocarbon intermediates such as ethylene, propylene, benzene, and cyclohexane. These hydrocarbon intermediates are then typically selectively oxidized using various processes to produce the desired chemical. For example, crude oil is refined into cyclohexane which is then selectively oxidized to “KA oil” which is then further oxidized for the production of adipic acid, an important industrial monomer used for the production of nylon 6,6. Many known processes are employed industrially to produce these petrochemicals from precursors found in crude oil. For example, see Ullmann's Encyclopedia of Industrial Chemistry, Wiley 2009 (7th edition), which is incorporated herein by reference.
For many years there has been an interest in using biorenewable materials as a feedstock to replace or supplement crude oil. See, for example, Klass, Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, 1998, which is incorporated herein by reference. Moreover, there have been efforts to produce adipic acid from renewable resources using processes involving a combination of biocatalytic and chemocatalytic processes. See, for example, “Benzene-Free Synthesis of Adipic Acid”, Frost et al. Biotechnol. Prog. 2002, Vol. 18, pp. 201-211, and U.S. Pat. Nos. 4,400,468, and 5,487,987.
One of the major challenges for converting biorenewable resources such as carbohydrates (e.g. glucose derived from starch, cellulose or sucrose) to commodity and specialty chemicals is the selective removal of oxygen atoms from the carbohydrate. Approaches are known for converting carbon-oxygen single bonds to carbon-hydrogen bonds. See, for example: U.S. Pat. No. 5,516,960; U.S. Patent App. Pub. US2007/0215484 and Japanese Patent No. 78,144,506. However, each of these known approaches suffers from various limitations and we believe that, currently, none of such methods are used industrially for the manufacture of specialty or industrial chemicals.
There remains a need for new, industrially viable catalysts for the selective and commercially-meaningful conversion of carbon-oxygen single bonds to carbon-hydrogen bonds, especially as applied in connection with the production of chemicals from hydroxyl-containing, dicarboxylate substrates (e.g., aldaric acids), and especially for the production of chemicals from polyhydroxyl-containing dicarboxylate substrates (e.g., glucaric acid) to important chemicals such as adipic acid.